You and your partner are both very strong to have been shouldering these woes, and you're certainly not alone in this. I'm glad your partner is beginning to seek help and I would stronlgly recommend he continue and see a psychologist when he is ready. Medications can be really hit and miss and it's important the the GP know what works and what doesn't work as soon as possible.
It's important to repeat what you've already suggested, none of this is your fault and you certainly haven't failed. I'm certain in saying that your partner probably doesn't know how talk about this inside his own head, giving voice to those thoughts is even more difficult.
Most of all, your partner has to want to help himself, your being with him is a tremendous support in itself. It is for that reason that I would encourage he seek psychological help to start negotiating this and seeing what his self and his sexuality in his mind might actually look like.
Good luck, stay strong!